In order to create various light effects and mood lighting in connection with concerts, live shows, TV shows, sport events or as a part on architectural installation light fixtures creating various effects are getting more and more used in the entertainment industry. Typically entertainment light fixtures creates a light beam having a beam width and a divergence and can for instance be wash/flood fixtures creating a relatively wide light beam with a uniform light distribution or it can be profile fixtures adapted to project image onto a target surface.
Light emitting diodes (LED) are, due to their relatively high efficiency, low energy consumption, long lifetime, and/or capability of electronic dimming, becoming more and more used in connection with lighting applications. LEDs are used in lighting applications for general illumination such as wash/flood lights illuminating a wide area or for generating wide light beams e.g. for the entertainment industry and/or architectural installations. For instance like in products like MAC101™, MAC301™, MAC401™, Stagebar2™, Easypix™, Extube™, Tripix™, Exterior 400™ series provided by the applicant, Martin Professional a/s. Further LEDs are also being integrated into projecting systems where an image is created and projected towards a target surface. For instance like in the product MAC 350 Entrour™ provided by the applicant, Martin Professional a/s.
Different kinds of LEDs are currently commercially available. For instance LEDs may be provided as colored LEDs emitting light having a relatively narrow spectral bandwidth and thus emitting light of a single color. Typically LED based lighting products include a number of these LEDs of different colors and light generated by the LEDs provided are combined into an outgoing light beam. The intensity of each color can be adjusted relatively to each other whereby the color of the outgoing light beam can be varied as known in the art of additive color mixing. These lighting products can thus create any color within the color gamut defined by the color of the LEDs. Typically this kind of lighting products include red LEDs, green LEDs and blue LED and are known as RGB lighting products. The RGB lighting products can produce red, green and blue by turning the LED of only one color on while turning the remaining colors off. Further the RGB products can produce white light by turning all colors on (and approximately at the same intensity) at the same time. However the color rendering index (CRI) of the white light is very low due the fact that the white is created by combining light with a narrow spectral bandwidth. The consequence is that an object illuminated by this white light, is not reproduced in its natural colors (as it appears when illuminated by sun light).
LEDs are also provided as white LEDs adapted to emit light having a board spectral bandwidth and these may further be provided with different color temperature. These LEDs have a high CRI, as they emitted light over a large spectral bandwidth and are thus used in LED based lighting products to create bright white light, which can be used to illuminate objects and reproduce the objects in substantially its natural color. However LED based lighting product based on white LEDs cannot create colored light beams without using a color filter as known in the art of subtractive color filtering.
RGBW LED based lighting products, where a number of single color LEDs and a number of white LEDs are combined, are also provided in order to be able to create different colors using additive color mixing and to improve the CRI and the efficacy of the white light. This is achieved by replacing a number of the colored LED with a number of the white LEDs. The white LEDs provide light having a broad spectral bandwidth and the CRI of the white light produced by such device is thus improved by white LEDs and the intensity of the white light is also increased. However the down side it that the intensity of the situated colors are reduced since there are fewer of these.
The LEDs are also provided in packages having a multiple amount a LED dies emitting light of different color and additionally also a led die emitting white light. The LED dies can be controlled individual, whereby the relative intensity of the light emitted by each dies may be varied in relation to each other whereby the color of the outgoing light can be varied as known in the art of additive color mixing. Typically these LED packages includes a red die, green die, blue die and a white die and are known as RGBW 4in1 LEDs. The RGBW 4in1 LED are often used in RGBW LED based lighting products as described above.
In general it is desired to have a multi-colored LED lighting product with a high lumen and also a high CRI. However this is hard to achieve with the LED types describe above as it due to Etendue limitations is not possible to combine light from an unlimited amount of light sources into a light beam. The known LED based lighting products are as a consequence often designed for specific purposes and it is often necessary to have a large range of LED based lighting products in order to be able to provide a large variety of lighting solutions. This is especially the case in connection with projecting systems, where the light is coupled through an optical gate, where an image creating objects (GOBO) is positioned. An optical projecting system collects the light from the optical gate and is adapted to image the optical gate (and thus also the image creating object) at a target surface. The light beam is very narrow when it passes the optical gate and such projecting systems are thus limited by Etendue. The Etendue, E=A*Ω, at the gate through which light is emitted has a limited opening area A and the imaging optics only collect light from a limited solid angle Ω. For light sources the Etendue can be calculated in the same way, where A is the radiating area, and Ω is the solid angle it radiates into. Further it is also desired to have very compact illumination devices, which is difficult to achieve when more light sources are being integrated into the same illumination device.
In projecting systems the light is generally collected into an optical gate where the image is generated, and an imaging optical system projects the gate onto a target surface. WO0198706, U.S. Pat. No. 6,227,669 and U.S. Pat. No. 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LED in order to focus the light, for instance to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
U.S. Pat. No. 5,309,277, U.S. Pat. No. 6,227,669, WO0198706, JP2006269182 A2, EP1710493 A2, U.S. Pat. No. 6,443,594 disclose lighting systems where the light from a number of LEDs is directed towards a common focal point or focusing area, for instance by tilting the LEDs in relation to the optical axis (JP2006269182 A2, WO0198706, U.S. Pat. No. 5,309,277) or by using individually refracting means positioned in front of each LED (U.S. Pat. No. 6,443,594, U.S. Pat. No. 7,226,185B, EP1710493).
WO06023180 discloses a projecting system comprising a LED array with a multiple number of LEDs where the light from the LEDs is directed towards a target area. The LEDs may be mounted to a surface of a curved base.
Systems where a multiple number of light sources are arranged on a successive moving emission illumination unit, and where the light from the multiple number of light sources are successively coupled into an optical system are also known. The successive moving emission unit moves successive in relation to the optical system whereby different light sources are alternately placed in the optical system, such that light can be coupled into the optical system. Controlling means are adapted to turn the light sources on when they are placed in the optical system and turn the light sources off when they leave the optical system. One advantage of this kind of systems is the fact that the light sources can be overloaded (with current) as they only need to be turned on for a very short period of time (when they are positioned in the optical path). Further the light sources can be cooled when they are not turned on and positioned outside the optical system. For instance US2003/0218723, WO03/063477, JP2004004359 and US2004/0125344 disclose such systems. This kind of systems are rather complex in size and difficult to manufacture as the successive moving emission illumination unit must move continuously and fast in relation to the optical system which can be a challenge as power and control signals must be feed to the light sources. Further the size of such system become relatively large as the large number of light sources takes up much space and only a very few light sources are used for the illumination purpose. US2007/0109501 discloses an illumination apparatus illuminating an objective illumination region. The illumination apparatus comprises a plurality of illuminants having light-emitting surfaces radiating diffused light, an illuminant substrate in which the illuminants are disposed so as to be set in array on the circumference, at least one optical member configured to guide the diffused light to the objective illumination region. A movable section is configured to drive the optical member so as to be rotatable around the center of the circumference serving as a rotation center, and a lighting control section configured to control a light-emitting timing of the plurality of illuminants. The movable section and the lighting control section operate together such that the quantity of light per unit time of the diffused light guided to the objective illumination region is within a predetermined range. The illuminants are embodies as red, green and blue LED and the optical member rotates continuously in relation the LEDs and collects light from the LED alternately. As a consequence the optical member collects only light form a limited amount of light sources which can be used in the later optical system. Further the light sources are alternately switched/turned on an off and can thus be overloaded (with current) during operation. The illumination apparatus discloses by U2007/0109501 provides an alternative solution to the rotating color wheels known form video projectors. Further the optical members are embodied as an L-shaped light rod where the collected light are reflected forwardly by using total internal reflection. However even, that in theory not loss occurs in total internal reflection the reflection surface introduces a great loss of light since not all light will hit/imping the reflective surface of the optical member within the critical angle required for total internal reflection. Further the illumination apparatus disclosed by US2007/0109501 are rather big as the illumines are arranged circumference at a distance from the optical axis. Another fact is that the CRI of the light created by this illumination apparatus is very bad due to the fact the only red, green and blue led are used. US2009/059557 relates to a similar system.
The prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low, as it is fundamentally only possible to effectively utilize light sources of same or less Etendue as the imaging optics in this kind of optical system. So if the source Etendue is a close match to the Etendue of the imaging system there are no gains in using multiple sources in order to increase the light output (intensity/lumen) as the Etendue of the light sources then will be larger than the Etendue of the imaging system and the imaging system is thus not capable of collecting the light.
Furthermore, a large amount of light is lost as the prior art fixtures typically only couple a central part of the light of the light beams through the gate in order to provide a uniform illumination of the gate, which again reduces the efficiency. The space in light fixtures is often limited and it is difficult to fit many light sources into prior art fixtures, for instance because the optical components associated with the light sources often take up a lot of space. Yet another aspect is the fact that color artifacts often appear in the output from fixtures having light sources of different colors. The reason for this is the fact that high performance LEDs used for stage-illumination have large, rectangular die areas of 1-12 mm2 and even higher This implies, that it is not possible to model the primary optics to a point source since the size-ratio between the primary optics and the LED die can get rather small. Furthermore, the rectangular shape can also be imaged in the output as rectangular patches. Compared to discharge lamps, these patches are ill fitted to smoothly fill out the circular spot profiles of stage-illumination instruments.